Lyme disease, the most frequent arthropod-borne disease in the USA, involves the skin, the central nervous system, the joints as well as other organs. The etiologic agent, Borrelia burgdorferi, is transmitted by ticks of the genus Ixodes. In its developmental cycle, the spirochete can be found adhered to the epithelial cells of the midgut. The midgut stage of the spirochete is essential for its development and also a vulnerable stage is their association with these cells could be inhibited. In the vertebrate host, spirochetes are preferentially found in tissues (skin, CNS and joints). Preliminary cell binding assays have shown spirochetal affinity for epithelial, glia and synovial cells from vertebrate organs. Each one of these spirochete-cell interactions represents a crucial step in the pathogenesis of Lyme disease. In this proposal, we will identify and characterize the spirochetal antigens which mediate cytoadherence (to tick midgut epithelium, cultured epithelium, rat oligodendroglia and rat synoviocytes). Identification of the spirochetal antigens will be done by cell adherence assays and by competitive inhibition with monoclonal antibodies and the antigens themselves. Characterization of the spirochetal antigens will be carried out to the determination of their amino acid composition, their N-terminal amino acid sequence, and if possible to the identification of the receptor binding domains of the adhesion molecules of B. burgdorferi. The neuropathogenesis of Lyme disease with its demyelinizing features is not well understood. In this proposal, cultured rat oligodendroglia will be used to detect injury at the cellular and molecular levels by measuring alterations in the structure and function of these cells and in their specific products or markers following interaction with spirochetes. Finally, the spirochete cell binding antigens will be isolated and used to immunize laboratory animals. Antigens associated with attachment to tick cells will be used to immunize rats (for nymphs) and rabbits (for adults) to determine if spirochetes can be eliminated or reduced in the midgut of the vector. The antigens associated with binding to vertebrate cells will be used for immunizing rats to follow the development of the antibody and cell mediated responses.